The invention relates to a method for the directed solidification of a molten metal, such as nickel for example, poured into a mold, by moving the mold out of a heating chamber and immersing the mold into a molten metal bath of lower melting point than the molten metal in the mold and serving as a quenching metal, aluminum for example. The invention furthermore relates to a casting apparatus for the practice of this method.
Such a method and such casting apparatus are subject matter of U.S. Pat. No. 4,108,236. The immersion of the mold in the molten quenching metal serves, by means of an intense axial heat flow as the casting hardens in the mold, to achieve a solid-liquid zone of the least possible depth and a very flat phase boundary between solid and liquid transversely of the main length of the casting, so that the crystals will grow axially in the casting. Directing in this manner requires keeping the radial loss of heat by radiation above the molten quenching metal as low as possible. For this purpose, in the known casting apparatus, a heat barrier generally known as a baffle is provided on the bottom of the melting chamber and is directed at the mold. In addition, a separating plate of a thermal insulating material floats on the quenching metal and has an opening for immersing the mold into the quenching metal. The thermal insulation is only imperfect, especially when the castings have several downwardly directed parts, since then the baffle and the separating plate cannot reach the areas between these parts. Aside from this, there still remains a gap between the mold and the baffle through which heat is radiated away.
U.S. Pat. No. 3,635,279 shows a container for immersion of a mold having a molten metal that is to be cooled, with a quenching melt whose surface is covered with a thermal insulating layer. This layer has the purpose of preventing any oxidation or excessively great cooling of the quenching melt. Upon its immersion into the quenching melt the mold penetrates this thermal insulating layer. It is not, however, moved out of a heating chamber.
In a process of this kind, DE-B-22 42 111 (to which U.S. Pat. No. 3,763,926 corresponds) discloses providing the surface of the quenching melt so closely beneath the heating chamber that the quenching plate of the mold dips at least partially into the quenching melt before the mold is submerged. Thus the quenching plate is cooled just when the mold is filled with the quenching melt, so that it exercises an especially good quenching action. For the prevention of heat losses between the bottom end of the heating chamber and the mold, a heat shield is provided.